In organ transplantation therapy, conventionally, various immunosuppressive agents are used in order to suppress rejection after organ transplantation. These immunosuppressive agents include, for example, tacrolimus (FK506) and ciclosporin A (Jpn J Pharmacol, 71, 89-100, 1996). However, conventional immunosuppressive agents have disadvantages including intense adverse effects such as growth stimulation of cancer cells and myelosuppression; infectious diseases and even the need of lifelong administration (Nonpatent Literature 1: Transplantation, 58, 170-178, 1994).
Further, determining a withdrawal time of an immunosuppressive agent is generally difficult. For example, tissue engraftment may be achieved without continued administration of an immunosuppressive agent. In that case, casually continued administration of an immunosuppressive agent may cause damage to a patient simply due to toxicity.
On the other hand, discontinued administration of an immunosuppressive agent may cause successfully engrafted tissue to start showing rejection. In this case, restarted administration of an immunosuppressive agent is often not effective to suppress rejection.
Meanwhile, various studies of organ transplantation have been conducted. For example, successful engraftment of a transplant without administering an immunosuppressive agent has been reported in a rat orthotopic liver transplantation (OLT) system, when donor DA rat liver (MHC haplotype RT1a) having a high transplant engraftment rate is transplanted to a recipient PVG rat (RT1c) (Nonpatent Literature 2: Transplantation, 35, 304-311-1983).
Further, there is a report that transplant rejection is suppressed by a single preoperative administration of blood serum of a recipient PVG rat having DA rat liver transplanted (post-OLT serum) to a transplant model system in a combination where rejection occurs (Nonpatent Literature 3: J. Surg. Res., 80, 58-61, 1998).
Further, disclosed is that rejection is suppressed and a recipient is survived by postoperative administration of anti-histone H1 polyclonal antibody to a cardiac transplant system (inch vivo) of a DA (RT1a) and LWIS rat (RT1L) in which rejection certainly occurs (Nonpatent Literature 4: Transplantation, 77, 1595-1603, 2004).
Furthermore, some of the present inventors have disclosed that mixed lymphocyte culture reaction (MLR) is suppressed by using post-transplant initial blood serum from PVG rat, and the anti histone H1 antibody shows MLR suppressive activity (Patent Literature 1: Japanese Patent Laid-Open No. 2004-149507).
Moreover, some of the present inventors have disclosed that anti histone H1 monoclonal antibody is produced, and the anti histone H1 monoclonal antibody produced by hybridoma 16G9 (Deposition Number FERM BP-10413) binds to a peptide consisting of an amino acid sequence represented by SEQ ID NO: 1 obtained by the phage display method (Patent Literature 2: WO2006/025580).
Even further, some of the present inventors have reported that a polyclonal antibody is produced, an antigen of which is a peptide consisting of an amino acid sequence represented by SEQ ID NO: 1 (Patent Literature 3: US-2009-0081247-A1).
However, creating a monoclonal antibody having excellent immunosuppressive activity which can be used to suppress transplant rejection in organ transplantation is still needed.